Contaminating or spreading disease through germs or bacteria; or metaphorically spreading influence like 'infecting others with enthusiasm.'
From Latin 'inficere' (to dip in, taint), from 'in-' (in) plus 'facere' (to make). Originally meant staining or tainting, then specifically meant spreading disease from the 1500s onward.
Before germs were discovered, people thought disease spread through 'miasma' (bad air)—doctors didn't realize they were infecting patients by not washing their hands between autopsies and surgeries until the 1800s!
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